Method of using a variable force compactor

ABSTRACT

A head is positionable close to a supported composite material. A compactor on the head is movable relative to the head by a fluid actuator. A programmable valve means ports air into the actuator at several different pressures to provide variable compaction force.

This application is a division of application Ser. No. 08/271320, filedJul. 6, 1994, now U.S. Pat. No. 5,738,749, which is a continuation ofSer. No. 08/068,017, filed May 27, 1993, abandoned.

FIELD OF THE INVENTION

In general, this invention relates to machines which lay compositematerial onto a surface, where it is desirable to compact strips havingtails, i.e., trailing sections of material which are less than fullstrip width. In particular, this invention relates to compaction ofcomposite tape by a compactor having at least two levels of compactionforce.

BACKGROUND OF THE INVENTION

In the field of advanced composite where a composite tape of fiberreinforced resin is laid on a tool to create laminated structures suchas aircraft parts, it is necessary to lay progressive runs of tape atangles other than 90° and 0° with the tool. When laying cross plies, forexample at 45°, it is often necessary to cut the end of the tape stripat some angle other than 90° with the tape length, and a problem mayarise when a primary compacting member spans adjacent pieces, which arecarried on a backing.

PRIOR ART

U.S. Pat. No. 4,557,783, of R. J. Grone et al, issued Dec. 10, 1985,addresses the problem of tail compaction in a composite tape layingmachine. The machine and compaction device are shown herein as Prior ArtFIGS. 1, 2a, 2b, and 2c. The entire disclosure and teaching of the '783patent is expressly incorporated herein by reference. Prior art FIG. 1depicts a high rail gantry tape laying machine 10 wherein a tape layinghead 11 is transported coordinately on horizontal side rails 12 andtransverse gantry rails 13 under a program commanded by a numericalcontrol (NC) unit 14. A contoured tape laydown surface 15, or tool, ispositionable with respect to the tape laying head 11 to form laminatedcomposite structures. The tape laying head 11 comprises, in part, a mainframe 16 supporting a tape supply reel 17. The supply reel 17 carries atape structure 18 comprising a filamentous composite tape and a paperbacking. The tape structure 18 is trained under a tape compactor unit 19and backing is accumulated on a take-up reel 20, in a manner well-knownin the art. The tape laying head 11 is movable along a vertical, orZ-axis 21 to adapt to changing tool heights along the tape path, and theentire tape head 11 is rotatable around the vertical axis 21. FIG. 2adepicts a schematic of the tape laying head 11 movable in a direction"X" with respect to a tool 22. The tape laying head 11 has a supply reel17 which feeds out a tape structure 18 comprising a composite tape 23releasably attached to a backing 24 such as a paper strip. The tapestructure 18 feeds through a cutter unit 25 and tape guide chute 26 toits lowermost position, adjacent the tool 22, where it then passes undera presser shoe or primary compactor 27 of the tape compactor unit 19. Asthe tape 23 is pressed against the laydown surface 28 of the tool 22,the backing 24 is separated and pulled onto the take-up reel 20 on thehead 11. Since the compactor 27 will ultimately see a tape tail 29, asdepicted in FIG. 2b, and since the compactor 27 presses against thebacking 24 in order to force the tape 23 against the laydown surface 28,it is obvious that the following section 30, complementary to the tail29, would also be stuck down if there were only one compactor 27. Toobviate this difficulty in handling the tail 29, the prior art tape head11 includes a tail compactor 31, which is a roller 32, carried on apivotable bell crank 33. The bell crank 33 is swung from a pivot joint34 on the head 11 by a cylinder 35, reacting against the head 11, todrive the tail compactor 31 against the tape 23 in the manner shown inFIG. 2c. The tail compactor 31 is located at a spot between the backing24 and the previously laid tape 23a, so that it contacts only tape 23when swung into the "down" position. Through linkage 36 attached fromthe bell crank 33 to the primary compactor 27 and to a backing guide 37,the downward stroke of the tail compactor 31 with respect to the tapelaying head 11 forces the primary compactor 27 and entire tape head 11up, away from the laydown surface 28, and the linkage 36 also moves thebacking guide 37 into a position to help steer the backing 24 on its wayto the take-up reel 20.

Certain features are noteworthy: Since the primary compactor is affixedto the tape head, the primary compaction force is provided by the headitself. And, since the tail compactor is thrust into position byreaction against the tape laying head, the tail compaction force islikewise provided by the head itself. Additionally, the primary and tailcompactors, as depicted, are spaced from one another along a horizontalplane, and this may prohibit application of the head to certaincontoured parts which deviate substantially from a flat surface, alongthe tape length.

U.S. Pat. No. 4,954,204, of M. N. Grimshaw, issued Sep. 4, 1990, teachesa presser member for contoured surfaces, and the entire disclosure andteaching of the '204 patent is expressly incorporated herein byreference. The '204 device is depicted herein as Prior Art FIGS. 3, 4,5a, 5b, and 5c. With reference to Prior Art FIG. 3, the '204 patentteaches a presser member 38 which is affixed to the bottom of a tapelaying head 11, as a primary compactor, but wherein the primarycompaction force is obtained from an actuator 39 (See FIG. 4) within thedevice itself; thus the presser member elements move with respect to thetape head 11. The presser member elements comprise a shoe plate stack40, i.e., plurality of adjacent shoe plates 41 of common cross-section(see FIG. 4), which may adapt to contours occurring across the tapestrip 23. The presser member 38 is a four-bar linkage of thedouble-slider type, where a horizontal slider 42 is connected by acontrol link 43 to a vertical slider (the shoe plate stack 40). Thepresser member 38 has a housing 44, quarter-rounded at its lower rearsurface and hollowed out to accommodate detail pieces. The top of thehousing supports a centrally located air cylinder 45, having a pistonrod 46 extending frontwardly, i.e., to the right of the figure.Immediately adjacent the front of the cylinder 45 is a pair of parallelguide rods 47a,b, one at each side of the assembly. The horizontalslider 42 rides on the guide rods 47a,b, and the end of the piston rod46 is affixed to the slider 42.

FIG. 4 shows the shoe plates 41 in relation to the control link 43 and acontrol rod 48 which extends through the shoe plates 41. At the interiorof the housing 44 is the actuator 39 for biasing the plates 41downwardly, away from the housing 44. The actuator 39 is a closedbladder spring, where a chamber 49 is faced with a flexible membrane 50which contacts the top edges of the shoe plates 41. Pressurized fluid isducted into the chamber through a port 51 to load the compliant membrane50 against the shoe plates 41.

FIG. 5a is a diagrammatic view of the elements of FIG. 3, showing thequarter-round housing 44 supporting the vertically movable shoe platestack 40, with a latch finger 52 "up" and the slider 42 moved to theright against the latch finger 52. The control link 43 is shownconnected to the control rod 48 which evens out, or "nulls" all platesat a known dimension, Z'. The downward biasing force provided by themembrane 50 is depicted as a bladder spring 53 reacting against the topedge of the shoe plates 41. The position of the elements in FIG. 5a isused for programming all vertical, or Z-axis dimensions, providing aknown point from which the shoe plates 41 may float up and down. FIG. 5bdepicts elements of FIG. 5a in an alternate position, where the latchfinger 52 is "down" and the slider 42 is moved leftwardly to thefully-retracted position. This position of the presser member 38 is usedfor compacting a tape strip 23 against the tool laydown surface 28. Thecontrol link 43 has moved the horizontal control rod 48 to anintermediate position within the shoe plate slot 54; the shoe plates 41are free to float on tool contours as the bladder spring 53 biases theentire shoe plate stack 40 against the tape 23. FIG. 5c depicts thelatch finger 52 retracted, and the slider 42 now fired to thefully-advanced position, all the way to the right. The control link 43now pulls the control rod 48 to a new raised position, thusfully-retracting the vertically-movable shoe plates 41 upwardly into thehousing 44, compressing the biasing bladder spring 53. This positionpermits the use of auxiliary equipment, such as a tail compacting roller55.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a compactor assemblyfor composite material, and method of use, wherein a primary compactoris independently powered with respect to a machine head and combinedwith a secondary compactor which is likewise independently powered withrespect to the head, and where at least one of the compactors may beoperated with at least two different levels of compaction force.

Another object of the present invention is to provide a composite tapestrip compactor assembly, and method of use, in which a main compactoris adaptable to contour changes occurring across the tape strip and atail compactor is capable of tail compaction on surfaces deviatingsubstantially from a flat plane along the tape length, and where atleast one of the compactors may be operated with at least two differentlevels of compaction force.

Another object of the present invention is to provide a compactorassembly for composite tape, and method of use, in which a maincompactor is utilized for laying essentially a full-width tape strip ata tape laydown point defined with respect to a tape laying head, and inwhich the main compactor is displaced by a tail compactor which mayfinish laying the tail of the tape strip at the tape laydown point, andwhere at least one of the compactors may be operated with at least twodifferent levels of compaction force.

Still another object of the present invention is to provide a compactorassembly for composite tape, and method of use, wherein main compactionand tail compaction occur at substantially the same point with respectto the tape laying head which carries the compactor assembly, and whereat least one of the compactors may be operated with at least twodifferent levels of compaction force.

A still further object of the present invention is to provide acompactor assembly for composite tape, and method of use, whereinprimary tape strip compaction and tail compaction are independent oftape laying head movement and are provided by the same actuator, carriedby the tape laying head, and where at least one of the compactors may beoperated with at least two different levels of compaction force.

Another object of the present invention is to provide a compactorassembly for composite tape, and method of use, in which linkage isutilized for simultaneously switching positions of the main compactorand tail compactor with respect to a tape laydown point, and where atleast one of the compactors may be operated with at least two differentlevels of compaction force.

The foregoing objects are achieved by the invention which is embodied ina method for compacting composite materials, comprising the followingsteps: placing composite material on a support surface; positioning acompaction frame proximal said support surface; providing a compactionelement on said frame between said frame and said material; providing afluid actuator between said element and said frame; porting pressurizedfluid into said actuator; applying a first compaction force to saidmaterial with said compaction element; varying the pressure of saidpressurized fluid; and applying a second compaction force to saidmaterial with said compaction element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art tape laying machine.

FIG. 2a is a side elevational view of a prior art compactor assemblyperforming a main compaction operation.

FIG. 2b is a plan view of a prior art tape strip having an angled tail.

FIG. 2c is a side elevational view of the prior art compactor assemblyof FIG. 2a, performing a tail compaction operation.

FIG. 3 is a side elevational view of a prior art compactor.

FIG. 4 is a front elevational view, in partial section, taken along theline IV--IV of FIG. 3.

FIGS. 5a, 5b, and 5c are diagrammatic views of the prior art compactorof FIG. 3.

FIG. 6 is a side elevation of a tape compactor assembly.

FIG. 7 is a front elevational section, taken along the line VII--VII ofFIG. 6.

FIG. 8 is a rear view, taken in the direction of arrow VIII of FIG. 6.

FIG. 9 is an elevational section, taken along the line IX--IX of FIG. 6.

FIG. 10 is a sectional view, taken along the line X--X of FIG. 6.

FIGS. 11a, 11b, and 11c are diagrammatic views of the tape compactorassembly of FIG. 6.

FIG. 12 is an elevational section, taken along the line XII--XII of FIG.11b.

FIG. 13 is an elevational section, taken along the line XIII--XIII ofFIG. 11c.

FIG. 14 is a side elevational view of a tape compactor assembly.

FIG. 15 is an elevational section through a tape compactor, illustratinga work surface having a valley.

FIG. 16 is an elevational section through a tape compactor, illustratinga work surface having a peak.

FIG. 17 is a diagrammatic view, in perspective, showing a compactionroller on a tape tail.

FIG. 18 is a graph plotting compactor air pressure vs. tape tail length.

FIG. 19 is an elevational section through a segmented compactor forcomposite material.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It should be noted that certain attitudinal references are employedherein, e.g., "horizontal", "vertical", and the like. Such referencesare only for the convenience of the reader, and the machine structure isnot so limited; those skilled in the art will appreciate that thespatial ordinates of the machine may be changed to suit a variety oftasks within the scope of the invention.

With reference to FIG. 6, a tape head 60 is shown with an improved tapecompactor assembly 61 affixed to its bottom surface. The tape head 60 isof a type which may be used with the tape laying machine 10 of FIG. 1.The tape compactor assembly 61 will move in a forward direction "X" withthe tape head 60, to the right of the FIG., when laying tape 23, and thehead 60 thus has a front end 60a, at the right of the FIG., and a rearend 60b to the left of the FIG. The assembly 61 includes a housing 62which is quarter-rounded at its lower rear surface and hollowed out toaccommodate detail pieces (not shown). The top surface of the housing 62has a frame 63 affixed thereto, which extends frontwardly. The frame 63serves as a mounting for an air cylinder 64, which has a piston rod 65extending frontwardly. The frame 63 also supports a pair of parallelguide rods 66a,b, one at each side of the assembly 61, and a horizontalslider 67 rides on the guide rods 66a,b and extends across the housing62 from side-to-side (see also FIGS. 7 and 8). The slider 67 is affixedto the piston rod 65.

The horizontal slider 67 has three specific positions:

(1) fully-retracted, as in FIGS. 6 and 11a;

(2) forwardly-advanced against a latch finger 68, as in FIG. 11b; and

(3) fully-advanced to the right with the latch finger 68 retracted, asin FIG. 11c.

The latch finger 68 is powered in vertical directions by a compact fluidcylinder unit 69 secured to the bottom of the frame 63. Each side of thehousing 62a,b has a vertical slider 70, constrained to move within avertical track 71 along a vertical centerline 72 defined on the housing62. Within the housing 62, immediately behind the vertical slider 70, isa main compactor 73. As shown in FIG. 9, the main compactor 73 comprisesa shoe plate stack 74 for contacting the backing 24 of a tape structure18. The shoe plate stack 74 is a plurality of parallel, wafer-like shoeplates 75 guided for vertical movement with respect to one anotherwithin the housing 62 and with respect to the housing 62. A verticalelongate slot 76 of common size is provided in line through all of theplates 75, and a control rod 77 extends horizontally, from side to sidethrough all of the slots 76 and is affixed to the vertical sliders 70.In the position shown in FIGS. 6, 9, and 11a, the control rod 77 ispositioned approximately mid-way along the vertical slot 76 so it willnot interfere with compactor movement which may require the shoe plates75 to adapt to a variety of contours across the tape width. This is thenormal tape laying position. When it is desired to land the compactor 73and tape 23 on a work surface 78, at the beginning of a tape laying run,the horizontal slider 67 is stopped against the latch finger 68 asdepicted in FIG. 11b. In this position, the upper edges 76a of the slots76 will rest on the raised control rod 77, causing the bottom edges 75aof the shoe plates 75 to be in line as shown in FIG. 13. This positionis an alignment, or "null" position, setting the bottom edges 75a of theplates 75 at a known relationship to the machine coordinates, forprogramming purposes.

In order to provide a downward biasing force to all of the plates 75, abladder spring 79 has been devised, in the manner of U.S. Pat. No.4,954,204, wherein the housing 62 has a closed chamber 80 formedimmediately above the shoe plate stack 74. The chamber 80 includes a-flexible membrane 81 extending across the shoe plates 75, in contactwith and spanning the top edges 75b. The chamber 80 is provided with anorifice 82 so that air or other fluid medium may be introduced into thechamber 80 and, thus, pressurize the membrane 81 to provide a downwardbiasing force to the entire stack of plates 75. The membrane 81 isyieldable, to accommodate surface contour variances which will cause theplates 75 to shift vertically, relative to one another, as the tape 23is laid.

In the preferred embodiment, the air valve unit 82a (FIGS. 15 and 16)employed to pressurize the bladder spring 79 produces a pressure outputwhich varies in proportion to the magnitude of an electrical signal.Such a valve unit is the Pneutronics VIP-FLEX Pressure Control unit,available from LDI Pneutronics Corp., Hollis, N.H. 03049. Therefore,this valve unit 82a may be controlled in accordance with an NC programto vary air pressure and consequent force directed against the tape 23.As an example, compaction of full-width tape may be performed at aconstant pressure. Next, unit loading on a tapered tail may be keptconstant by changing the total downward force acting on the tailcompaction roller; i.e., by varying air pressure in accordance with thetail profile.

It will be appreciated that in some instances, it may be desirable tosupply only a fixed pressure to the bladder spring 79. It may also bedesirable to supply two alternative pressures to the bladder spring 79;a first pressure for main compaction, and a second pressure for tailcompaction.

With reference back to FIG. 6, a flexible sheet or skid 84 is attachedto the front of the housing 62, and directed around the nose, or bottomedge 75a of the shoe plates 75 to present a smooth surface against thebacking 24. It may be appreciated, however, that some embodiments mayomit the skid 84. The skid 84 is guided around the quarter-roundsection, within a surface channel or relief 85, and is held taut by astrap 86. The strap 86 is affixed to the skid 84 and tensioned by acoiling device 87 carried on the tape laying head 60. The tape structure18 is shown coming from the tape guide chute 26 to the tape lay-downpoint 88 established by the intersection of the vertical centerline 72and a horizontal plane 89 defined on the work surface 78. At the tapelaydown point 88, while the head 60 continues moving to the right, tape23 is deposited on the work surface 78, and the backing 24 is separatedfrom the tape 23 and pulled upwardly against the skid 84, while runningto a take-up reel (not shown).

The roller 90 depicted in FIG. 6 is a tail compactor, and is locatedbetween the tape 23 and the backing 24, trailing the tape laydown point88, in the manner taught in U.S. Pat. No. 4,557,783, Prior Art FIG. 2a.The roller 90 is shown in its home position, swung all the way to theleft.

A tail compactor is a secondary compactor used for compacting tape ofless than full width. The roller 90 is carried at one end of a firstelongate link 91, which is pivotally connected at its other end to thevertical slider 70 about a first horizontal pivot axis 92. Thehorizontal slider 67 has a depending section 67a at each side of thehousing 62 (see FIG. 7) which extends approximately midway down thehousing 62, and a second elongate link 93 is pivotally connected at oneend to the horizontal slider 67 about a second horizontal pivot axis 94while its other link end is pivotally connected to the first link 91about a third horizontal pivot axis 95 lying approximately midwaybetween the ends of the first link 91. The first link 91 also includes acam follower 96 which extends horizontally from the link 91 into a camslot 97 provided on the housing 62 (see also FIG. 10). The cam slot 97governs the first link 91 and, consequently, movement of the tailcompaction roller 90 as the horizontal slider 67 is driven by the 5cylinder 64. The cam slot 97 is arcuate and upwardly arched, from itsinitial portion, thereafter sloping downwardly towards the verticalslider 70. And, while the cam follower 96 is accurately guided withinthe cam slot 97 for most of the path, the end of the slot 97 isrelieved, as will be described later in connection with FIG. 11c. Whilethe first and second links 91,93 under discussion are shown on one side62a of the housing 62, i.e., facing the viewer, it will be appreciatedthat there are identical links 91,93 on the opposite side 62b of theassembly 61, and the tail compaction roller 90 spans the first links 91,as shown in FIG. 8.

Compactor Operation

Operation of the compactor assembly 61 may be appreciated by referringto diagrammatic FIGS. 11a-11c.

FIG. 11a depicts the elements of FIG. 6, where the latch finger 68 is"down" and the slider 67 is moved leftwardly to the fully-retractedposition. In this position, the main compactor 73 or shoe plate stack 74is biased against a tape backing 24 which is being stripped from tape 23laid to the laydown surface 78, and the position of the vertical slider70 and its control rod 77 is such that the rod 77 will not hindervertical float of the plates 75 (see also FIG. 9). The bladder spring 79biases the entire shoe plate stack 74 against the backing 24 and tape23, and the shoe plates 75 can float in compliance with contourvariances occurring across the tape width.

FIG. 11b depicts the housing 62 with the latch finger 68 "up" and thehorizontal slider 67 moved to the right, against the latch finger 68. Inthis position, the vertical slider 70 is driven upward slightly so thatits control rod 77 evens out, or "nulls" all plates 75 at a knowndimension, Z' (see also FIG. 12). The position of the elements in FIG.11b is utilized for programming all vertical, or Z-axis dimensions.

FIG. 11c depicts the latch finger 68 "down", and the horizontal slider67 now fired to the fully-advanced position, all the way to the right.The vertical slider 70 is now driven to a new raised position where itscontrol rod 77 drives the vertically-movable shoe plate stack 74 to afully-retracted upward position into the housing 62, compressing thebladder spring 79 (see also FIG. 13). The skid 84 will follow along withthe stack 74. Simultaneous with this movement of the vertical slider 70,in response to horizontal slider link 91 is first elongate link 91 isswung to a nearly vertical position, governed through most of itsmovement by the cam follower 96 traveling in the cam slot 97, so thatthe tail compaction roller 90 will be switched into the region of thetape laydown point 88, previously occupied by the now-retracted maincompactor 73 (shoe plate stack 74). The linkage, coupled with guidanceprovided by the cam follower 96, insures that the tail compaction roller90 will move along a path which will not interfere with the substantialslope (approximately 15°) of the work surface 78 with respect to thehorizontal plane 89. With reference to FIG. 13, the tail compactionforce is accomplished by the same bladder spring 79 which provides themain compactor force. The compressed bladder spring 79 attempts to drivethe control rod downward along with the vertical slide 70, and thevertical slide 70 in turn, drives the first elongate link 91 and roller90 downward against the tape tail 23a. The sides 97a,b of the cam slot97 are slightly flared for clearance (see also FIG. 14) when the camfollower 96 is positioned as in FIG. 11c, so the first link 91 androller 90 may move vertically relative to housing 62 against the tail23a.

Thereafter, as the tape head 60 is lifted from the work surface 78 inanticipation of another tape laying run, the horizontal slider 67 isretracted to the left, causing the tail compaction roller 90 to swingback out to its home position, and permitting the main compactor 73(shoe plate stack 74) to descend.

FIGS. 6-9 depict an ideal situation for the invention, where it isassumed that the vertical slide 70 will move upward easily when thehorizontal slide 67 is actuated. It is further assumed that the camfollower 96 moves without shake in the cam slot 97. In actual practice,though, frictional forces are present, and the cam slot 97 at each side62a,b, of the housing 62 is manufactured with clearance; therefore, toensure quick action and smoothness, a practical embodiment of theinvention is further developed in FIG. 14, where the following featuresmay be seen:

1. The cam slot 97 is formed into a cam plate 98 bolted to the sides62a,b, of the housing 62; this simplifies machining and heat treatment,as well as alignment of the right and left side elements.

2. A spring-loaded plate 99, slidable on shoulder screws 100, spans thehousing 62 and is biased downwardly by springs 101 guided on theshoulder screws 100. The plate 99 contacts a roller 102 which isclevis-mounted within the first link 91, just above the cam follower 96.The spring-loaded plate 99 keeps shake out of the assembly 61 while thetail compaction roller 90 is in its home position, and provides impetusfor the first portion of its advancement to the tape laydown point 88.

3. The top portion of the vertical slider 70 is provided with ahorizontal stud 103 which carries an antifriction roller 104. A bracket105 on the sides 62a,b of the housing 62 supports a helper cylinder 106.The cylinder 106 has a short-stroke piston rod 107 linked to a lever 108pivotally-mounted to the bracket 105. The lever 108 extends under theroller 104 and serves to provide an initial lifting force for thevertical slider 70, to overcome friction as the horizontal slider 67 isactuated. Once moving, the mechanical advantage of the horizontal slider67 over the vertical slider 70 increases, and the assist provided by thelever 108 is no longer needed. The piston rod 107, lever 108 and roller104 are all outside of the first link 91, to avoid interference.

4. The second link 93 is comprised of two link ends 93a,b, connected bya stud 109, threadably received therein, and a locknut 110 secures theassembly once the proper dimension between the second and third pivotaxes 94,95 has been established.

Those skilled in the art will appreciate that the vertical slider 70 maybe provided with antifriction elements in certain applications.Similarly, provision of antifriction elements within the varioussliders, pivot joints and rollers herein, are deemed to be well withinthe ken of the machine designer.

It may be noted that, while the actuator for the main compactor 73comprises a bladder spring 79, having a closed chamber with a membranecovering, it is also anticipated that the membrane 81 may be omitted,and fluid pressure may be applied directly against the top of the shoeplate stack 74 to bias the stack 74 in a downward direction.

It is further contemplated that a resiliently faced element may besubstituted for the main compactor 73, and other devices may besubstituted for the tail compaction roller 90.

The sectional view depicted in FIG. 15 shows certain elements of FIG. 9,wherein the main compactor 73, or shoe plate stack 74 is showndistributed across a tape strip 200 laid in a valley 201 of a worksurface 202. In general, more compaction force is needed to compact thetape strip 200 into the valley 201, than is needed to compact the tapestrip 200 on a flat surface. In this case, therefore, the valve unit 82ais modified by command from the NC unit 14 to port a higher pressure P₁into the bladder spring 79 than is required for normal flat laying runs.As stated before, the air valve unit 82a receives a supply of air orother fluid from a supply line 203, and is easily modulated or changedin response to an NC program, since the machine programmer will be wellaware of the tool contours and tape strip placement requirements. Asfurther illustration of the desirability of having a programmable airpressure and consequent programmable compaction force capability, FIG.16 depicts the elements of FIG. 15 when changing to a profile which hasa peak 204 occurring across the tape width. Here, a lesser compactionforce is needed than is required to lay the tape strip 200 into a valley201 per FIG. 15, and consequently, the valve unit 82a is managed byfurther instruction from the NC unit 14 to reduce the pressure from thatof FIG. 15 to a reduced pressure, P₂.

The use of a main compactor 73 as in FIGS. 15 and 16, is not confined toa tape laying machine (see FIG. 1); but is adaptable to other machineswhich apply composite material to a support surface; for example, afiber placement machine as depicted in U.S. Pat. No. 5,022,952, of M.Vaniglia, issued Jun. 11, 1991. The entire disclosure and teaching ofthe '952 patent is herein expressly incorporated by reference.

FIG. 17 discloses a sequence drawing, in perspective, of application ofa variable force tail compactor 205 to a linearly tapering tail 206 of acomposite tape strip 207. In this case, for illustration purposes, fivepositions are shown along the tape tail 206 where it is desired tomaintain a constant unit loading on the tail material with a tailcompaction roller 90 which extends for the full width of the tape 207.In this case, therefore, the force applied to the roller 90 shoulddecrease linearly from the beginning 208 of the tape tail 206 to the end209. The five positions depicted illustrate force levels F₁, F₂, F₃, F₄and F₅, which correspond to pressure levels P₁, P₂, P₃, P₄ and P₅. Apressure distribution graph 210 is shown in FIG. 18, where the pressurevaries linearly for the length of the tail, "L". Thus, the valve unit82a is programmed for variable pressure along the tail 206. Withreference back to FIGS. 9 and 13, the tail compaction force is providedto the roller 90 by the bladder spring 79, pressurized by the valve unit82a.

The application of a variable force compactor to a variety of compositematerials and machines is further facilitated by a reference to U.S.Pat. No. 4,869,774, of J. Wisbey, issued Sep. 26, 1989, which disclosesa segmented compactor 211 which finds application in both tape layingand fiber placement machines. The entire disclosure and teaching of the'774 patent is expressly incorporated herein by reference. FIG. 19depicts a segmented compactor 211 from the '774 patent, which has areference roller 212 at its center position flanked by adjacent slidingrollers 213 which may move relative to the fixed reference roller 212.In this case, the actuator 214 for pressurizing the movable rollers 213is also supplied with air from the valve unit 82a, and regulated by anumerical control program within the NC unit 14.

While the invention has been shown in connection with a preferredembodiment, it is not intended that the invention be so limited. Ratherthe invention extends to all such designs and modifications as comewithin the scope of the appended claims.

What is claimed is:
 1. A method for compacting composite tape,comprising the following steps:placing the composite tape on a supportsurface; positioning a compaction assembly proximal said supportsurface; providing a first compaction element on said assembly betweensaid assembly and said tape; providing a second compaction element onsaid assembly between said assembly and said tape; providing a fluiddriven actuator on said assembly for commonly actuating said first andsecond compaction elements; directing pressurized fluid to said actuatorto actuate said first and second compaction elements and applycompaction force to said tape; sequentially actuating said first andsecond compaction elements; applying a first compaction force to saidtape with said first compaction element in response to actuation of saidelement; applying a second compaction force to said tape with saidsecond compaction element in response to actuation of said element; andtransferring between said first and said second compaction elementswhile maintaining compaction force on said tape on said support surface.2. A method for compacting composite material comprising the stepsof:positioning a compaction assembly, comprising a first compactionelement, a second compaction element and a fluid actuator, commonlyactuating said first and said second compaction elements, proximal asupport surface; placing the composite material between said supportsurface and the first and second compaction elements; selectivelyactivating said first compaction element for placing said compositematerial on said support surface; placing the composite material on thesupport surface; directing pressurized fluid to the actuator;selectively applying a compaction force to the composite material bysaid actuator acting on the first compaction element; selectivelyactivating the second compaction element; selectively applying acompaction force to the composite material by said actuator acting onthe second compaction element.
 3. The method according to claim 2further comprising the step of varying the pressure of the pressurizedfluid directed to the fluid actuator.
 4. The method according to claim 3wherein the composite material is a composite tape.
 5. The methodaccording to claim 2 further comprising the step of selectively varyingthe pressure of the pressurized fluid directed to the fluid actuator. 6.The method according to claim 5 wherein the composite material is acomposite tape.
 7. The method of claim 2 further comprising the step ofvarying the compaction force applied to the composite material by theactuator acting on the first and second compaction elements.
 8. Themethod of claim 2 further comprising the step of varying the compactionforce applied to the composite material by the actuator acting on thesecond compaction element.
 9. The method according to claim 2 whereinthe composite material is a composite tape.